Various polymer materials have been used for cables and the like in order to provide electric insulation. The polymer materials for the cables require proper electrical properties and durability to continuously provide initial performance. Particularly, the cables used for vehicles require high mechanical properties, high thermal resistance, high flame retardancy, abrasion resistance, and the like. Cable manufacturers have improved productivity by increasing cable extrusion rate, therefore, cover materials of automotive cables need to satisfy extrusion processability as well as the required properties described above.
Currently used automotive cables are classified by CLASS A (continuous operating temperature of 80° C., PVC) and CLASS B (continuous operating temperature of 100° C., cross-linked PVC) according to ISO 6722, an automotive international standard. However, cables of CLASS C (continuous operating temperature of 120° C.) or CLASS D (continuous operating temperature of 150° C.) having a more severe heat resisting condition need to be used since engine components generates high heat.
CLASS C mostly uses a cross-linked polyolefin (cross-linked PO; XL-PO)-based resin in which a polyolefin-based copolymer resin such as a polyethylene(PE) resin or an ethylene vinyl acetate resin is irradiated by an electron beam and cross-linked, and CLASS D or higher uses a fluorine-based resin and a silicone-based resin having a very excellent thermal resistance. However, the resins used for CLASS D are high-priced, and molding such as extrusion is not simple.
Accordingly, in the related art, flame retardancy has been enhanced by adding a large quantity of flame retardants since polyolefin-based resins themselves have high combustibility, however, there is a decrease in mechanical and physical properties. CLASS C (continuous operating temperature of 120° C.) has been domestically commercialized in some countries, however, the use of CLASS D (continuous operating temperature of 150° C.) material has not been developed. As a result, the development of insulating materials of CLASS D for automotive cables having low costs and simple extrusion molding at an ultrahigh speed of 1,000 MPM or higher is necessary.
Moreover, the use of halogens, heavy metals, and the like has been inactive due to their impact on environment pollution. The use of a decabromodiphenylether (commonly called as decabro, DBDE) brome-based flame retardant exhibiting relatively superior flame retardancy in a polychloride vinyl (PVC) or polyolefin resin are banned in several European countries as the material may generate dioxin.
Automotive cable industries are actively coping with globally reinforced environment regulations. For example, in Europe, restriction of hazardous substances (RoHS), sales of electrical and electronic products using 6 hazardous materials (Pb, Cd, Cr6+, Hg, polybrominated biphenyl (PBB), Polybrominated Diphenyl Ethers (PBDEs)) are banned from Jul. 1, 2006. In US, the use of PBDEs, a flame retarding material, is restricted from 2008. In Japan, J-MOSS is implemented from 2006, environment regulation is reinforced, and in Korea, “ecomark” labelling system, is reinforced on environmental friendly products and the like.
Accordingly, metal hydroxides such as aluminum hydroxide (Al(OH)3) and magnesium hydroxide (Mg(OH)2) or phosphorous-based flame retardants have been used.
Korean Patent No. 341112 relates to a polyolefin flame retarding and insulating composition for high temperature, and in particular, an insulating material for high temperature having improved thermal resisting properties in polyolefin-based non-toxic (non-halogen) flame retarding materials used for insulating materials and the like. Specifically, in the composition, a hindered phenol-based antioxidant is added in 0.1 to 10 parts by weight, a thioester-based antioxidant in 0.1 to 5 parts by weight, a phenol-based metal non lubricant in 0.1 to 5 parts by weight, a benzimidazole-based or its zinc salt-based antioxidant in 0.1 to 20 parts by weight, and a hindered amine-based stabilizer in 0.1 to 5 parts by weight with respect to 100 parts by weight of the resin mixed with one type or 2 to 4 types of polyolefin-based resins. An inorganic flame retardant of which surface is treated with vinyl silane is used in 80 to 150 parts by weight with respect to 100 parts by weight of the resin, and a flame retardant aid is used in 1 to 50 parts by weight with respect to 100 parts by weight of the resin. However, this insulating composition is an irradiation cross-linking type and has high initial investment costs, thereby limiting the use of a moisture cross-linking type.
Korean Patent No. 729012 discloses a moisture cross-linking flame retardant resin composition for producing an insulating material as an inorganic flame retardant formed with magnesium hydroxide and aluminum hydroxide of which surface is treated with any one material selected from among vinyl silane, stearic acid, oleic acid, aminopolysiloxane, and a polymer resin. However, when these materials are applied for cables, oil resistance capable of enduring in severe conditions is not high, and a large quantity of non-halogen-based flame retardant is used in order to provide a high degree of flame retardancy, therefore lacking thermal resistance and flexibility since properties such as specific gravity, hardness, and flection, and thus, causing cracks.
For that reason, an insulating material composition for cables having high thermal resistance in which halogen elements are not included and having excellent properties such as mechanical properties, high thermal resistance, high flame retardancy, and abrasion resistance is necessary.
The above information disclosed in this Background Art section is only for enhancement of understanding of the background, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.